Reaction Rate and Stoichiometry

Question

For the decomposition of hydrogen iodide on a gold surface at 150 °C

2 HI(g)H₂(g) + I₂(g)

the average rate of disappearance of HI over the time period from t = 0 s to t = 4248 s is found to be 1.20×10^-4 M s^-1.

The average rate of formation of I₂ over the same time period is_______  M s^-1.

Answer 1

the general outline of solving the problem:

(1) ALWAYS make sure the equation given is balanced [in this case, it is]

(2) label knowns and unknowns [knowns: 1.20×10^-4 M s^-1 and the time period (0-48 sec) // unknowns: rate of formation for I₂]

(3) notice the terminology of the problem at the end regarding when the I₂ is formed. It's formed in the same time period, so it can be inferred that these are the only two reactions taking place, in terms of decomposition.

(4) use the balanced equation to solve for I₂ average rate of formation by using the ratio between I₂ and HI. These ratios describe the moles of each species given.

(5) use dimensional analysis to figure out the average rate of formation for I₂

Mathematical Response:

(ALWAYS start with the given if you're lost on where to start, and work your way through the problem by following the relations between the known and the unknown)

(1.20×10^-4 M s^-1 ) x ( 1 mol I₂ / 2 mol HI ) = 6.00 x 10^-5 Ms^-1 (final answer)

*make sure to check sig figs at the end of the problem (it's reported correctly in the problem solved above)